Trans Adriatic Pipeline (TAP; Albanian: Gazsjellësi Trans-Adriatik, Azerbaijani: Trans Adriatik Boru Xətti Greek: Αδριατικός Αγωγός Φυσικού Αερίου, Italian: Gasdotto Trans-Adriatico) is a pipeline project to transport natural gas, starting from Greece via Albania and the Adriatic Sea to Italy and further to Western Europe.
The pipeline would be supplied by natural gas from the second stage of the Shah Deniz (Azerbaijan) gas field development in the Azerbaijani section of Caspian Sea through the South Caucasus Pipeline and the planned Trans Anatolian Pipeline (TANAP). Since it will enhance energy security and diversify gas supplies for several European markets, the TAP project is supported by the European institutions and seen as a "Project of Common Interest" and a part of the Southern Gas Corridor.
Trans Adriatic Pipeline project was announced in 2003 by Swiss energy company EGL Group (now named Axpo). The feasibility study was concluded in March 2006. Two options were investigated: a northern route through Bulgaria, the Republic of Macedonia and Albania, and a southern route through Greece and Albania, which finally was considered to be more feasible. In March 2007, the extended basic engineering for the pipeline was completed. Greece opposed for the route of the Trans Adriatic Pipeline passing through Albanian territory, as it would allow Albania to become transmission hub for gas in the Western Balkans.
On 13 February 2008, EGL Group and the Norwegian energy company Statoil signed an agreement to set up Trans Adriatic Pipeline AG, a joint venture to develop, build and operate the pipeline. In June 2008, the project company filed an application with the Greek authorities to build a 200 kilometres (120 mi) section of the pipeline from Thessaloniki to the Greek-Albanian border. In January 2009, the TAP project carried out a marine survey in the Adriatic Sea to verify the offshore route for the future gas pipeline. A route assessment survey in Albania started in July 2009. In March 2009, an intergovernmental agreement between Italy and Albania on energy cooperation mentioned TAP as a project of common interest for both countries. In January 2010, TAP opened country offices in Greece, Albania and Italy. In March 2010, TAP submitted an application to Italian authorities for inclusion into the Italian gas network.
In November 2010, TAP started a route refinement survey in northern Greece in preparation for the environmental impact assessment. On 7 September 2011, the Trans Adriatic Pipeline AG (TAP AG) submitted its EU Third Party Access Exemption applications in all three host countries. Exemption will allow TAP AG to enter into long term ship-or-pay gas transportation agreements with the shippers of Shah Deniz II gas. The exemptions were granted on 16 May 2013.
In February 2012, the Trans Adriatic Pipeline was the first project to be pre-selected and to enter exclusive negotiations with the Shah Deniz Consortium. In August 2012, consortium partners BP, SOCAR and Total S.A. signed a funding agreement with TAP's shareholders, including an option to take up to 50% equity in the project.
On 28 September 2012, Albania, Greece and Italy confirmed their political support for the pipeline by signing a memorandum of understanding.
In February 2013, Greece, Italy and Albania signed an intergovernmental agreement.
In June 2013, the project was chosen as a route for gas from Shah Deniz II over the competing Nabucco West project. Later in 2013, BP, SOCAR, Total, and Fluxys became shareholders of the project.
The pipeline starts at the Greece–Turkey border at Kipoi, Evros, where it will be connected with the Trans-Anatolian gas pipeline. It will cross Greece, Albania and the Adriatic Sea and come ashore in Italy near San Foca. The total length of the pipeline will be 878 kilometres (546 mi), of which 550 kilometres (340 mi) in Greece, 215 kilometres (134 mi) in Albania, 105 kilometres (65 mi) in offshore, and 8 kilometres (5.0 mi) in Italy. The offshore leg will be laid at a maximum depth of 810 metres (2,660 ft).
The initial capacity of the pipeline will be about 10 billion cubic metres (350 billion cubic feet) of natural gas per year, with the option to expand the capacity up to 20 billion cubic metres (710 billion cubic feet). It will use 48-inch (1,200 mm) pipes for pressure of 95 bars (9,500 kPa) on the onshore section and 36-inch (910 mm) pipes for pressure of 145 bars (14,500 kPa) on the offshore section.
TAP also plans to develop an underground natural gas storage facility in Albania and offer a reverse flow possibility of up to 8.5 billion cubic metres (300 billion cubic feet). These features will ensure additional energy security for the Southeastern Europe.
The „Interconnector“ (IGB) shall connect Greece with Bulgaria.
Trans Adriatic Pipeline AG is a joint venture company registered in Baar, canton Zug, Switzerland, with a purpose of planning, developing and building the TAP pipeline.  The Managing Director of the company is Luca Schieppati.
Shareholders of the Trans Adriatic Pipeline are BP (20%), SOCAR (20%), Snam (20%), Fluxys (19%), Enagas (16%) and Axpo (5%).
TAP is estimated to cost around EUR 4.5 billion.
The European Bank for Reconstruction and Development (EBRD) considers a USD 1.5 billion loan. "We are considering up to 500 million euros of our own money for TAP plus we will try to arrange with other banks up to 1 EUR billion in a syndicated loan," Riccardo Puliti, managing director of energy at the EBRD said.
On 6th February 2018, The European Investment Bank (EIB) voted to hand out EUR 1.5 Billion, one of Europe’s largest ever loans, to one of the EU’s largest fossil fuel projects, the Trans Adriatic Pipeline. 
There have been incidents of protests by both local citizens and government officials against the Trans Adriatic Pipeline.
In Italy the TAP requires construction of a gas terminal in a historical olive grove in the countryside near the Apulian town of Melendugno. The site boasts some century-old olive trees which are to be explanted and transferred to an alternative location in an operation that cannot guarantee the trees' survival. This has been criticised by the local public as well as environmentalists, also in relation to a deadly parasitic disease (Xylella fastidiosa) that has been affecting olive groves in the region for years, and can spread to previously unaffected areas with tree relocation.
Further, the pipeline's landing point on the Italian coast is located under the pristine beach of San Foca, a particularly beautiful and beloved summer destination for beachgoers. Locals and environmentalists have raised safety concerns regarding millions of cubic litres of compressed flammable gas being piped only 1.5 metres under a beach that will be kept open to the public and is bound to be packed with tourists, including children, during the summer months.
Some government officials, such as multiple mayors from the area and the governor of the region of Apulia, also supported the environmentalists' opinion that the pipeline might cause more harm than good and could be an opportunity for local organised crime and corruption to infiltrate public tenders for construction work on the Italian side. They worry especially in relation to a taxpayer-funded 60-kilometre long interconnector which will have to be built to link the TAP's Italian terminal in Melendugno to Italy's national gas network near the industrial port of Brindisi. The Apulia Region governor Michele Emiliano told an Al Jazeera English crew in 2016 that he could not understand why an alternative landing point to San Foca beach, closer to the Brindisi industrial area, was not chosen in spite of lower costs, less severe environmental impact, and proximity to pre-existing gas infrastructure.